DESCRIPTION (Investigator?s Abstract): The goal of this project is to determine the complete genome sequence of Streptococcus gordonii, a pioneering colonizer of dental plaque and significant causative bacterium for infective endocarditis. The formation of dental plaque is regulated by complex interactions between the dental surfaces of the host and the surface structures of S.gordonii and other oral bacteria. The basis of the interacting surface structures is highly specific adherence mechanisms controlled by adhesin-receptor partnerships and extracellular glucans. Infective endocarditis often occurs as a result of oral trauma and is likely dependent upon the production of proteases and additional virulence factors. Genetic recombination and transfer of adhesins, antibiotic resistance determinants and possible virulent factors between the oral streptococci may be responsible for evolution of adhesins/receptor pairs and development of antibiotic resistance in S.gordonii. Finally, S.gordonii has been shown to be an effective antigen-delivery vehicle for vaccine development. Through the identification of genome structure, novel adhesions/receptors and regulatory elements, this project will accelerate experimental work directed towards understanding the dynamics of S. gordonii in dental plaque formation and its role in infective endocarditis. The approach to sequencing Streptococcus gordonii strain Challis (NCTC7868) will be a modified whole genome random sequencing strategy successfully used at TIGR to completely sequence 14 prokaryotic genomes. The project will consist of four phases: 1) construction of random small and medium insert plasmid libraries and a large insert BAC library from S. gordonii strain Challis, 2) sequencing both ends of approximately 23,500 small and medium insert clones, 3) sequencing the ends of a set of minimally overlapping BAC clones to provide a scaffolding structure that will minimize the effort required for gap closure and provide confirmation of the underlying assembled structure, and 4) assembly and annotation of the genome to identify structural features, assign gene and functional roles to open reading frames based upon database similarity searches. The data developed from this study will be deposited in several databases, including the TIGR web site. In addition, all clone sets will be made available to the research community.